This is a fantastic add-on that really helps me use Firefox in the multiple ways I need to without having to log in and sync multiple Mozilla profiles, however, it's currently malfunctioning (23-Mar-2024). Thanks to olivrrstray's review I was able to get back in and I concur with JavitoPlay, the dev is most likely working to update it.

worked well before but is broken now

Now its broken the "click" on the profiles, but you can go to edit profiles, and "set as default" to open the profiles you had keep.

I suppose the developer is working to fix it

In general, this extension its great.

Broken

Broken with the March 19th update, 124.0.

Edit:
For the more tech savvy, there is a workaround on Issues tab on the Github page.

For the less tech savvy who have Windows:
1. Hit Windows + R.

2. Put "%APPDATA%\nulldev\FirefoxProfileSwitcher\config\" in the prompt, and hit "ok." This will open the folder with configuration files.

3. Copy the path; this is the address in the top bar. It should look similar to this:
C:\Users\[yourusername]\AppData\Roaming\nulldev\FirefoxProfileSwitcher\config

4. Open the notepad app, create a new file. Paste the following text in the notepad:
{"browser_binary": "C:\\Program Files\\Mozilla Firefox\\firefox.exe"}

5. Open the File menu, click Save As.

6. In the address bar, paste the address you saw before, and change "Save as type" from Text documents to all files. You should see files like "avatar.json"

7. Save the file as: config.json

8. Reopen Firefox

Was working well but now unresponsive, cannot access my other profile.

Update - fixed it thanks to olivrrstray's short guide.

It was working fine but recently my clicks have been non responsive. I'm locked out of my other profile and am unable to access any of my bookmarks

It worked fine until Firefox version 124. Now it doesn't react on when I want to switch profile.

GOOD

Took a minute to setup, but once done its an awesome experience! btw im on a Macbook Pro 2019 Intel I7

Works flawlessly on m2 pro macbook running Sonoma, honestly insane that this hasn't been implemented natively yet

Unclear and confusing in Fedora

Work really nice on Windows 11. Really solve the multi-profile browser problem. But need some installing some .exe extension from github.

For those with FF 124.0 that broke this plugin. Here's how to fix this temporarily:

1. Hit Windows + R.
2. Put "%APPDATA%\nulldev\FirefoxProfileSwitcher\config\" inside the prompt, and hit "ok." This will open the configuration folder. The address should look like this:
C:\Users\[yourusername]\AppData\Roaming\nulldev\FirefoxProfileSwitcher\config
You should see avatar.json and profile-options.json
3. Right click anywhere inside the "config" folder, and create new text document. Name it "config.json".
4. Open config.json (with notepad) and paste the following text into config.json:
{"browser_binary": "C:\\Program Files\\Mozilla Firefox\\firefox.exe"}
5. Save.
6. Reopen FF.

credits to: olivrrstray

Works well but requires some initial setup and basic knowledge of how Firefox profiles work. It would be nice if this extension allowed users to upload their own profile picture and/or offered the option of using each Firefox account's avatar as the profile picture.

Requires unsigned code to be installed.

Please make this work with forks of firefox, e.g. LibreWolf or Waterfox. You have plenty of people on your github describing the issue, who have been reporting it for months.

I followed the instructions but in the end the switcher didn't work (Ubuntu 22.04).